Report on the NIST Cryptographic Key Management Workshop

This is a belated report on the Cryptographic Key Management Workshop that was held by NIST on September 10-11. Karen Lewison and I went to Washington DC for the workshop, where we presented a talk on techniques for addressing the key management challenges of derived credentials.

Cryptographic key management may seem to be a dry topic, but the workshop was quite interesting, especially the second day, which looked at the future. It was attended by about 50 cryptographers, and was webcast. It began with a fascinating keynote address by Whitfield Diffie on the history of cryptographic key management. His presentation is online, but slides cannot do justice to the wealth of stories and anecdotes that he narrated.

A Framework for Designing Cryptographic Key Management Systems

The main purpose of the workshop was to discuss the current drafts of NIST Special Publication 800-130, and NIST Special Publication 800-152 and solicit comments on them. (Instructions for sending comments on draft NIST publications can be found at http://csrc.nist.gov/publications/PubsDrafts.html.) SP 800-130 is a comprehensive framework of topics that should be considered by anybody who has to specify a Cryptographic Key Management System (CKMS); since key management is an essential aspect of cryptography, the framework should be invaluable to anybody designing a system that incorporates cryptographic functionality. SP 800-152 profiles the framework for cryptographic key management systems that will be used in US Federal agencies, but goes beyond the systems themselves to cover their procurement, installation, management, and operation.

The two publications were discussed during the first day of the workshop. I cannot possibly go over the very detailed discussions that took place, so I will limit myself to repeating one comment I made regarding Section 4.7 of SP 800-130, “Anonymity, Unlinkability and Unobservability”, and expanding upon it.

Anonymity, unlinkability and unobservability are privacy features that may not be directly relevant to the authentication of Federal employees in the course of their work, but they are very relevant to the authentication of both consumers on the Web at large, and citizens who access Federal information systems. Traditional authentication by username and password provides these three privacy features; but passwords have well-known security and usability drawbacks, one of them being the difficulty of remembering many different passwords. One way of reducing the number of passwords to be remembered is to rely on a third-party identity provider (IdP), so that one password (presented to the IdP) can be used to authenticate to any number of relying parties. The Federal Government allows citizens to access government web sites through redirection to several Approved Identity Providers.

But third party login has privacy drawbacks. In usual implementations, anonymity is lost because the relying party learns the user’s identity at the IdP, unlinkability is lost by the use of that identity at multiple relying parties, and unobservability is lost because the IdP is informed of the user’s logins. Profiles of third-party login protocols approved for citizen login to government sites mitigate some of these drawbacks by asking the identity provider to provide different identities for the same user to different relying parties. This mitigates the loss of anonymity, and the loss of unlinkability to a certain extent. (Relying parties by themselves cannot track the user, but they can track the user in collusion with the IdP.) But the loss of unobservability is not mitigated, because the IdP is still informed of the user’s activities.

I believe that the Government should work to develop and promote authentication methods that eliminate passwords while preserving anonymity, unlinkability and unobservability. Cryptographic authentication with a key pair, using different key pairs for different relying parties, can be a basis for such methods.

A Look at the Future

The second day of the workshop featured presentations on capabilities of future cryptographic key management systems, ranging from innovative to futuristic. (Both days’ presentations can be found in the workshop web page.)

Tim Polk, manager of the Cryptographic Technology Group at NIST, motivated the talks that followed by going over challenges identified during the development of the CKMS framework, related to interoperability across security domains, algorithmic agility, constrained devices, privacy, and scalability. He also stressed the need to develop CKMSs that are resilient to quantum computing attacks before it is too late.

Dennis Branstad of NIST discussed security policies, stating as a goal their automated specification, negotiation and enforcement.

Anna Lysyanskaya of Brown University discussed her work on anonymous credentials. She mentioned a new technique for revocation of anonymous credentials that was presented at Crypto 2012 by Libert, Peters and Yung, and said she thought it deserved the best paper award. I believe a full version of the conference paper can be found at http://eprint.iacr.org/2012/442. I haven’t read the paper yet. Revocation of privacy-enhancing credentials is practically difficult; I have discussed the topic in several earlier posts.

Paul Lambert of Marvell Semiconductors discussed authentication and privilege management for devices connected by wireless area networks. I was glad to hear him propose the use of a raw key pair as a credential. I later proposed the same thing in the talk on derived credentials.

Lily Chen of NIST discussed the difficult key management problem of handing over a secure link as a smart phone travels from one network to another, when the networks use technologies that may be as different as UMTS and WiFi.

Sarbari Gupta of Electrosoft discussed key management in a cloud environment. She argued that the Federal Risk and Authorization Management Program (FedRAMP) does not have sufficient requirements for secure key management, and advocated the establishment of a Federal Profile for Cloud Key Management.

Elaine Barker of NIST went over the intricacies and subtleties of random bit generation, and solicited comments on Draft Special Publication 800-90B (entropy sources) and Draft Special Publication 800-90C (RBG Constructions, DRBGs and NRBGs). Comments are due December 3rd.

Rene Struik discussed a method of secure key storage and true random number generation using physical unclonable functions (PUFs). The idea is to use accidental properties of a device to generate a unique key when the device is turned on. (So I would say that his technique is closer to key generation than key storage.) Error correction is used to remove minor differences in subsequent key generations. As an additional benefit, those differences are used for random number generation. This very interesting work is related in multiple ways to our own work on mobile authentication and derived credentials; I plan to discuss it in more detail in the next blog post.

Mary Theofanos of NIST went over two case studies of usability of key management procedures: a PKI deployment, and a PIV pilot. My personal getaways: the designer of a key management system must know the users and their mental models of security; must provide multiple authentication methods, e.g. by retaining username-password as a backup for a cryptographic credential; and must not require frequent PIN changes.

The usability talk was followed by a panel that presented three use cases of cross-domain interactions. Bob Griffin of RSA discussed key management in the cloud. Saikat Saha of SafeNet discussed virtualized hardware security modules. John Leiseboer of Quintessencelabs discussed quantum key distribution; this was the first presentation I’ve attended related to quantum cryptography, and it motivated me to find out more about this futuristic topic.

Derived Credentials

Finally, I gave a presentation on mobile authentication and derived credentials, co-authored with Karen Lewison. Even though this was the last presentation at the end of a long day of talks, I was gratified that, as far as I know, nobody snuck out early to the Dogfish Head brewery across the street from the NIST campus 🙂 . Derived credentials is a NIST concept referring to credentials that, in the future, will be installed in a mobile device after the user of the device authenticates with a PIV card. Our presentation went over three techniques for implementing derived credentials that we proposed earlier in a blog post and a white paper, viz. public key cryptography without certificates, key pair regeneration as an alternative to tamper resistance, and encapsulation of cryptographic and biometric processing in a “prover black box” and a “verifier black box” to insulate app developers from the complexities of cryptography and biometrics.

But we also went beyond derived credentials, in response to a request made by Elaine Barker on behalf of Dennis Branstad before the workshop. We discussed extensions of our techniques, for authentication across security domains, for social login without passwords, and for data protection at rest without tamper resistance. Since then we have put online a whitepaper on the data protection work. We have not yet written whitepapers on authentication across security domain or social login without passwords.

Wrap-up

Tim Polk wrapped up the workshop by encouraging everybody to send comments. Although there is an official comment period for each draft publication, NIST welcomes comments at any time.

Like the workshop on privacy-enhancing technology I attended last year, this workshop was both enjoyable and very useful. I’m glad to be on the email distribution list, and I’m looking forward to the next cryptography workshop at NIST.

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